1. Field of the Invention
The present invention relates to a variable valve device for an internal combustion engine in which at least one kind of switching oil passages are provided in a pair of rocker shafts while oil pressure of the switching oil passage of one of the rocker shafts is introduced to the switching oil passage of the other rocker shaft to switch rocker arms located in the rocker shafts at the same time.
2. Description of the Related Art
The engine which is switched from a normal state to a high-speed mode or a cylinder suspension mode using the variable valve device with the rocker arm is being developed to balance improvement of output characteristics and reduction of fuel consumption in an automobile-mounted reciprocating engine (internal combustion engine). When the engine enters a high engine revolution speed range, the engine is switched to the high-speed mode suitable to the high engine revolution speed range. The engine is switched to the cylinder suspension mode in which some of cylinders are suspended, when the engine enters a running condition in which large output is not required.
In the cylinder suspension mode, frequently lifts (open and close) of inlet and exhaust valves of the cylinder are stopped to decrease pumping loss. Therefore, in most variable valve devices, the inlet valve is driven by a hydraulic rocker arm which can switch the inlet valve among the normal mode (low-speed mode), the high-speed mode, and the cylinder suspension mode, the exhaust valve is driven by a hydraulic rocker arm which can switch the exhaust valve between the normal mode (low-speed mode) and the cylinder suspension mode, and the rocker arms are driven by the different oil-pressure systems. For example, Jpn. Pat. Appln. KOKAI Publication No. 2005-90408 discloses this kind of technique.
Specifically, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-90408, in the inlet and exhaust rocker shafts (pair), two kinds of switching oil passages for high-speed mode and cylinder suspension mode are formed in an axial direction in the inlet-side rocker shaft. The switching oil passage for cylinder suspension mode is formed in the axial direction in the exhaust-side rocker shaft.
Further, two oil-pressure systems are used. One oil-pressure system comprises the switching oil passage for cylinder suspension mode of the exhaust-side rocker shaft and the switching oil passage for cylinder suspension mode of the inlet-side rocker shaft. These passages are connected in series. Another oil-pressure system is used for high speed switching.
In the two oil-pressure systems, when the oil pressure does not act on the switching oil passage for high-speed mode and the exhaust-side switching oil passage, the low-speed mode (cam selection suitable to the normal running) is selected in both the inlet-side and exhaust-side rocker arms.
When the oil pressure is applied only to the switching oil passage (for high-speed mode) of the inlet-side rocker shaft, the inlet-side rocker arm is switched to the high-speed mode (cam selection suitable to the high-speed running). When the oil pressure is applied only to the exhaust-side switching oil passage (for cylinder suspension mode), the inlet-side and exhaust-side rocker arms are switched to the cylinder suspension mode (the lift of inlet and exhaust valves is suspended) in which the cam displacement is not transmitted to the valve.
In the variable valve device, because the mode is frequently switched according to the running state of the engine (automobile), there is demanded a performance of rapid mode switching in all the cylinders of the engine within predetermined switching time, i.e., a switching property.
As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-90408, in the system in which the oil pressure is introduced from one of the rocker shafts to the other rocker shaft, a large area of the passage is secured because the exhaust-side switching oil passage for cylinder suspension mode is provided only in the exhaust-side rocker shaft.
However, the inlet-side switching oil passage for cylinder suspension mode is arranged parallel to the switching oil passage for high-speed mode in the inlet-side rocker shaft, so that the area of the passage becomes smaller than that of the exhaust-side switching oil passage for cylinder suspension mode due to a structure.
Therefore, in the structure disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-90408, in which the oil pressure is supplied in series from the exhaust-side switching oil passage for cylinder suspension mode to the inlet-side switching oil passage for cylinder suspension mode, although the oil pressure is rapidly delivered to the exhaust-side rocker arm, the oil pressure is prevented from being easily delivered to the inlet-side rocker arm due to the difference in area of the passage.
Therefore, the inlet-side rocker arm, particularly the inlet-side rocker arm located at the end of the oil-pressure system is operated while delayed with respect to the exhaust-side rocker arm (at the start or end of the switching to the cylinder suspension mode).
The delay decreases the switching property during the cylinder suspension mode. Sometimes a switching fluctuation caused by the delay generates a noise and vibration. Furthermore, the influence of the delay narrows a range where the cylinder suspension mode is performed in engine.